As is known, the processing of metals (cutting, polishing, forming) as also processing in the oil drilling field, require the use of auxiliary fluids which generally consist of a mineral or synthetic oil as such or emulsified, optionally charged with solids (pastes, mud).
The residues of the processing fluid must be removed at the end of the processing, before passing to a subsequent phase where their presence would prevent its feasibility.
In the mechanical industry, for the washing of finished or semi-finished metal products contaminated by oils, emulsions and polishing pastes, non-flammable solvents are used, such as for example chlorinated products, which are toxic for the persons using them and also particularly harmful for the environment owing to the poor biodegrad-ability and their high ozone consumption potential (ODP) (B. P. Whim, B. G. Johnson xe2x80x9cDirectory of solventsxe2x80x9d page 173, 1997).
In the oil drilling field, steel pipes (casings) which are lowered into the well in the presence of oil mud must be washed before passing to the cementing phase.
In this case the washing of the mud-contaminated surfaces with solvents is at present carried out using solvents which are volatile, toxic, flammable, non-biodegradable and with a high content of aromatics such as carbon-naphtha, for example.
As far as the safety of the work-site and workers who are exposed to these solvents, is concerned, the competent authorities are issuing increasingly strict regulations and criteria for the production and use of solvents, but it is evident that the use of effective solvents which are non-flammable, atoxic, eco-compatible (biodegradable with a low ODP) and with a low volatility, not only provides a real solution to problems relating to personnel safety and respect for the environment, but also presents greater simplicity in the use, conservation and disposal of these solvents, which is reflected in the operating costs.
In accordance with this, great necessity is felt in the solvent field for the use of solvents which satisfy the above requisites at acceptable costs for application on an industrial scale. The chemical industry is therefore making considerable efforts to supply adequate solvents, as an alternative to the traditional ones.
It has now been found that organic carbonates can be effectively used as solvents for the washing in an open system of metal surfaces contaminated by fluids such as mineral oils, synthetic oils or their emulsions o/w optionally charged with solids, in order to obtain auxiliary fluids in the form of pastes or mud.
The present invention therefore relates to the use of organic carbonates as solvents for the washing of metal surfaces.
The invention also relates to a process for the washing of metal surfaces which consists in applying the solvent based on organic carbonates to metal surfaces and under suitable conditions for removing the contaminants present from the surfaces.
In particular, the organic carbonates described in the invention are represented by the following formula: 
wherein:
n=1-4
R and Rxe2x80x2 are two linear or branched alkyl radicals which contain a number of carbon atoms whose sum is equal to at least 5 and which can be the same or different.
Examples of carbonates which can be used for the invention are: methyl n-butyl carbonate, methyl n-pentyl carbonate, methyl iso-octyl carbonate, di-isopropyl carbonate, di-n-propyl carbonate, di-n-butyl carbonate, di-iso-propyl carbonate, di-iso-octyl carbonate.
The general characteristics of the di-alkyl carbonates object of the invention are: low solubility in water which is always less than 1,000 ppm and therefore also an excellent hydrolytic stability, Kauri-Butanol index equal to at least 150, flash point higher than 55xc2x0 C., boiling point higher than 145xc2x0 C. at atmospheric pressure.
The advantages obtained from using organic carbonates in this type of application are: effectiveness in removing contaminants, simplification of the equipment which uses them i.e. being able to operate in an open system as the emissions produced, owing to their characteristics (biode-gradability, low ODP and atoxic) and their reduced quantity, do not create any problems either for human beings or for the environment.
In accordance with this, they can therefore also be used in offshore drilling activities, such as for example, in the washing of casings where, in practice, a substantial hydrolytic stability of the solvent and in any case the non-toxicity of its degradation products are also required.
Corrosion inhibitors, non-ionic wetting agents and water for their application in emulsion, can optionally be added to the organic carbonates, object of the invention.
The solvents, object of the invention, are based on di-alkyl carbonates.
If these are produced by the trans-esterification of dimethylcarbonate (DMC) with higher alcohols, they are without halogens and free acidity deriving therefrom.
The alcohols which can be used for producing the di-alkyl carbonates object of the invention, have C3-C25 chains.
A criterion however, for selecting the alcohol, to ensure absolute compatibility of the di-alkyl carbonate deriving therefrom, also in the presence of traces of residual free synthesis alcohol and/or deriving from the degradation of the ester during use, is provided by the toxicological and eco-toxicological characteristics deriving from the structure of the alcohol itself.
Symmetrical or asymmetrical carbonates can be obtained when mixtures of at least two alcohols are fed to the trans-esterification.
In a preferred embodiment, the di-alkyl carbonate can be di-n-butyl carbonate (DnBC) or di-iso-octyl carbonate (DiOC) or their mixtures.
The solvent, object of the present invention, is preferably used pure as such, or is formulated to be subsequently applied in aqueous emulsion.
The formulate may optionally contain a corrosion inhibitor, a co-solvent and an emulsifying agent; it is generally preferable in the preparation of the formulate for the weight fraction of each of the additives not to exceed 20% w of the formulate.
The corrosion inhibitor can be selected from the group of amino-alcohols having tertiary nitrogen, such as for example, tri-ethanol (TEA).
The co-solvent can be selected from the group of glycol ethers; examples of co-solvent comprise propylene glycol methylether (PM), di-propylene glycol methylether (DPM) or di-propylene glycol n-butyl ether (DPNB).
The emulsifying agent can be selected from the group of non-ionic surface active agents, from the group of ethoxylated alcohols or acids, preferably using those of the C9-C18 aliphatic series which optimize the hydrophilic/lipophilic (HLB) ratio which characterizes them.
The conditions under which the washing of metal surfaces, object of the present invention, is carried out, can vary.
The washing is generally carried out at atmospheric pressure within a temperature range of 20xc2x0 C. to a maximum which is close to, but without exceeding, the flash point of the di-alkyl carbonate used.
The means of applying the solvent to the item to be washed, are not critical; in most cases simple immersion in a tank which does not necessarily have to be thermostat-regulated, is sufficient.
Mechanical actions such as manual application or spraying or also the use of ultra-sounds reduce the time required for the washing.
It should be noted however that the contact time required by the solvent also depends on a series of factors, such as the type of oil/grease to be removed, the formulation which contains it and the aging of the contaminant especially if in paste or mud form.
The contact times generally range from less than a minute to an hour; longer contact times however can be adopted without there being any risk of ruining the surface to be treated.